Conventionally, a seal member used for hermetically closing an opening portion of a substrate storage container with a cover has been formed to have an endless shape using one or some of various thermoplastic elastomers such as polyolefine elastomers and polyester elastomers, or various rubber materials such as fluororubber and EPDM (ethylene propylene diene terpolymer) by means of a mold. The thus obtained seal member for a substrate storage container is used after it has been cleaned so as not to contaminate substrates to be stored.
The conventional seal member has been used in such a manner that a fitting portion provided in the form of a groove or a projection at a peripheral edge of the opening portion of a container body or at a peripheral edge of a cover corresponding to the opening portion and an engaging portion provided in the form of a projection or a groove on the seal member are fitted to each other. Fitting of the seal member has been manually performed.
The conventional seal member is entirely formed of a thermoplastic elastomer or the like which is an elastic material as described above. For this reason, the seal member is easily deformable and its size varies widely depending on molding conditions or the like. In particular, the seal member is prone to stick to the mold after it has been molded, and if it is forcibly peeled off from the mold when it is released from the mold, a circumferential length thereof is further deviated. Furthermore, it is difficult to keep the shape of the seal member accurately during storage after it has been molded. Moreover, the conventional seal members lack size stability, for example, they are easily deformed due to uneven cooling caused by stacking of products or under different loads.
Since the seal member, as described above, is formed of an elastic and non-rigid material and it is required that a recess or projection serving as an engaging portion for engaging the cover or the container body be formed on the seal member, the seal member is more prone to stick to the mold, whereby it is difficult to automate removal of the seal member from the mold, so that the removal of the seal member must be performed manually.
Since the seal member obtained in the above manner is easily deformed even during storage thereof, as described above, the seal member must be handled with the utmost caution so as to prevent the seal member from deforming, resulting in handling thereof during storage or transferring being troublesome.
A seal member is used in a substrate storage container after it has been cleaned with a cleaning liquid such as a surface active agent or the like, or rinsing water such as pure water, ultrapure water or the like, whereby contaminants such as particles or the like on a surface of the seal member are removed from the seal member. In such cleaning, in order to increase productivity, a plurality of seal members are collectively processed. Unfortunately, since the conventional seal members formed of a flexible material having elasticity easily deform into an infinite variety of forms and are unstable, when they are cleaned without any arrangement therefor, a portion of a surface of the seal member is twisted or portions thereof overlap, so that sufficient cleaning can not always be achieved.
For this reason, a method for cleaning has been proposed, wherein a seal member is cleaned while the seal member is held on a frame formed to serve as a retaining member for cleaning so that a slight tension is exerted on the seal member. However, such a slight tension or changes in temperature during cleaning cause the size of the seal member to be unstable.
Furthermore, when the seal member is attached to the container body or the cover of the substrate storage container to be used, the engaging portion of the seal member must be properly fitted-in over its entire periphery, resulting in the attaching operation being very complicated. In particular, in the case of a substrate storage container which stores large diameter substrates such as wafers having a diameter of 200 mm or more, which have become mainstream recently, it is matter of course that the circumference of the opening portion of the container body is large, so that mounting of the seal member has become very troublesome work. However, in order to maintain the cleanliness of the substrate storage container, it is necessary to prevent interposition of a worker as much as possible, and thus it is preferable to handle the seal member by means of an automatic machine.
Also, when the seal member is mounted at a predetermined location on the container body or the cover of the substrate storage container, unless the seal member is properly fitted at at least one portion thereof, there is a possibility of the following undesirable events taking place: a poor sealing occurs; a part of the engaging portion of the seal member comes off from the fitting portion and is partially turned up when the cover is removed; subsequent fitting of the cover can not be performed due to the turned-up part of the seal member; and particles are produced due to rubbing of the seal member against a portion of the container when the seal member is strongly compressed at the turned-up part thereof or the like, to thereby contaminate the substrates to be stored.
Particularly, in recent years, mounting and dismounting of the cover of the substrate storage container has been performed by an automatic machine instead of the conventional work carried out by a person in order to improve cleanliness in a workshop. Accordingly, when there are variations in the circumferences of the seal members, deformation of the seal members, insufficient fitting of the seal member in mounting or the like, there will be troubles, namely, the seal member is bitten without a positional displacement of the seal member being made known, and the opening/closing operation of the cover is interrupted due to the occurrence of a load when the cover is closed, resulting in the problem that productivity has been considerably reduced.
The present invention has been made in order to solve the above problem. Therefore, an object of the present invention is to provide a seal member which varies within a small range in size during molding and has an excellent mold releasability, which is easy to handle during cleaning or storage thereafter and easy to mount to a substrate storage container and allows automation of these operations, which is less contaminated during handling, and which is prevented from being displaced from the engaged position or turned up during use by firmly mounting the seal member to the substrate storage container, and a substrate storage container using such a seal member.